LibArchive: Default initialize member variables

Problem:
- `memset` is used to initialize data instead of using default
  initialization.

Solution:
- Default initialize all member variables.
- Eliminate use of `memset` in favor of C++ braced initialization.

Userland/Libraries/LibArchive/Tar.h

@@ -117,22 +117,22 @@ public:
     void calculate_checksum();
 
 private:
-    char m_filename[100];
-    char m_mode[8];
-    char m_uid[8];
-    char m_gid[8];
-    char m_size[12];
-    char m_timestamp[12];
-    char m_checksum[8]; // an uninitialized header's checksum is filled with spaces
-    char m_type_flag;
-    char m_link_name[100];
-    char m_magic[6];
-    char m_version[2];
-    char m_owner_name[32];
-    char m_group_name[32];
-    char m_major[8];
-    char m_minor[8];
-    char m_prefix[155]; // zero out the prefix for archiving
+    char m_filename[100] { 0 };
+    char m_mode[8] { 0 };
+    char m_uid[8] { 0 };
+    char m_gid[8] { 0 };
+    char m_size[12] { 0 };
+    char m_timestamp[12] { 0 };
+    char m_checksum[8] { 0 }; // an uninitialized header's checksum is filled with spaces
+    char m_type_flag { 0 };
+    char m_link_name[100] { 0 };
+    char m_magic[6] { 0 };
+    char m_version[2] { 0 };
+    char m_owner_name[32] { 0 };
+    char m_group_name[32] { 0 };
+    char m_major[8] { 0 };
+    char m_minor[8] { 0 };
+    char m_prefix[155] { 0 }; // zero out the prefix for archiving
 };
 
 }

Userland/Libraries/LibArchive/TarStream.cpp

@@ -131,8 +131,7 @@ TarOutputStream::TarOutputStream(OutputStream& stream)
 void TarOutputStream::add_directory(const String& path, mode_t mode)
 {
     VERIFY(!m_finished);
-    TarFileHeader header;
-    memset(&header, 0, sizeof(header));
+    TarFileHeader header {};
     header.set_size(0);
     header.set_filename(String::formatted("{}/", path)); // Old tar implementations assume directory names end with a /
     header.set_type_flag(TarFileType::Directory);
@@ -148,8 +147,7 @@ void TarOutputStream::add_directory(const String& path, mode_t mode)
 void TarOutputStream::add_file(const String& path, mode_t mode, ReadonlyBytes bytes)
 {
     VERIFY(!m_finished);
-    TarFileHeader header;
-    memset(&header, 0, sizeof(header));
+    TarFileHeader header {};
     header.set_size(bytes.size());
     header.set_filename(path);
     header.set_type_flag(TarFileType::NormalFile);